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Segments of carotid artery from Wistar (NW), Kyoto Wistar (WKY), and spontaneously hypertensive rats (SHR) were used to compare mechanical properties and connective tissue composition. Pressure-diameter measurements were made under conditions of active (5 microgram/ml norepinephrine) and passive (0 mM Ca2+ and 2 mM EGTA) smooth muscle. Systolic blood pressures averaged NW, 121 +/- 3; WKY, 124 +/- 4; and SHR, 187 +/- 5 MMHg. Passive mechanics were stiffest in SHR and most compliant in NW arteries. No differences in collagen-elastin ratio were found but collagen + elastin was lowest in SHR and highest in NW carotids. These results are not consistent with current concepts of the contribution of connective tissue elements to passive mechanics. Maximum stress development was NW, 561 +/- 49; WKY, 735 +/- 50; and SHR, 944 +/- 79 X 10(3) dyn/cm2. Diameter reductions to NE at 100 mmHg were NW, 17.6 +/- 2.4%; WKY, 16.7 +/- 2.0%; and SHR, 24.8 +/- 2.4%. The former suggests different contractile protein contents or more efficient intercellular force coupling in SHR. The latter suggests a more effective contractile apparatus as a result of stiffer passive muscle elements and/or a relatively larger wall thickness.
R. H. Cox (Wed,) studied this question.